In data processing systems which use multiple modules, e.g., an array of peripheral drive modules, or units, such as data storage disks, it is sometimes necessary to replace one or more defectively operating drive modules. Normally, in order to do so, the operation of the entire array is suspended while the one or more defective modules are removed and one or more new modules are substituted. In effect, the system operation must be halted and no further data processing operations can occur with respect to the module array until the one or more new replacement modules are inserted and the states of each of the replacement modules are updated to conform to the state of the modules that have been replaced.
It is desirable to devise a technique wherein one or more defective modules of an array thereof can be removed and one or more new modules substituted therefor without shutting down the operation of the entire array so that all of the other modules remain in operation for whatever data processing operations are occurring. Such a technique should include the provision of an appropriate indication to the control processor which controls the operation of the modules that a removal operation is occurring. The technique should then permit a new module to be inserted into the array and then provide for an appropriate indication thereof to the control processor and for an operation by which the state of the new module can be updated to be the same as the state of the prior used module would have been if it had not needed replacement. Accordingly, the new module is then fully operative from that point on. Such an overall process can be referred to as a "hot repair" technique.